Distributed antenna system architectures

ABSTRACT

Communication system includes first unit; and second unit(s) having processing unit(s), downstream signal path(s), and upstream signal path(s). First unit communicates downstream digital transport signal (including digital representation of original downstream RF signal received at first unit) to second unit(s). Second unit uses processing unit and downstream signal path to generate downstream RF signal (for radiation from antenna) from downstream digital transport signal; and communicates upstream digital transport signal (generated from upstream RF signal received at second unit(s) using processing unit(s) and upstream signal path(s)) to first unit. Upstream digital transport signal includes digital representation of received upstream RF signal. Feedback path digitizes downstream RF signal(s) to provide digital representation(s) of downstream RF signal radiated from antenna to processing unit(s). Second unit pre-distorts input signal to downstream signal path for non-linearities in downstream signal path using digital representation of downstream RF signal radiated from antenna as received from feedback path.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/688,400 filed Aug. 28, 2017 and entitled“DISTRIBUTED ANTENNA SYSTEM ARCHITECTURES” (currently pending), which isa continuation application of U.S. patent application Ser. No.13/495,220 filed Jun. 13, 2012 and entitled “DISTRIBUTED ANTENNA SYSTEMARCHITECTURES” (issued as U.S. Pat. No. 9,748,906 on Aug. 29, 2017),which claims priority to U.S. Provisional Patent Application Ser. No.61/496,548, filed on Jun. 13, 2011, which are all hereby incorporatedherein by reference.

BACKGROUND

This disclosure relates to distributed antenna systems, repeaters,distributed base station systems, and the like.

SUMMARY

One embodiment is directed to a distributed antenna system comprising ahost unit and at least one remote antenna unit that is communicativelycoupled to the host unit. The host unit is configured to communicate adownstream transport signal from the host unit to the remote antennaunit. The remote antenna unit to which the downstream transport signalis communicated uses the downstream transport signal to generate adownstream radio frequency signal for radiation from an antennaassociated with the remote antenna unit. The remote antenna unit isconfigured to communicate an upstream transport signal from the remoteantenna unit to the host unit, wherein the upstream transport signal isgenerated from a received upstream radio frequency signal received atthe remote antenna unit. The remote antenna unit is configured toperform self-interference suppression processing in an upstream signalpath using, as an input thereto, a feedback signal derived from thedownstream radio frequency signal radiated from the antenna.

Another embodiment is directed to a remote antenna unit for use in adistributed antenna system. The remote antenna unit comprises atransport interface to communicatively couple the remote antenna unit toa host unit included in the distributed antenna system and to receive adownstream transport signal from the host unit. The remote antenna unitfurther comprises a processing unit coupled to the transport interface,at least one downstream signal branch, and at least one upstream signalbranch. The processing unit and downstream signal branch are configuredto use the downstream transport signal to generate a downstream radiofrequency signal for radiation from an antenna associated with theremote antenna unit. The transport interface is configured tocommunicate an upstream transport signal from the remote antenna unit tothe host unit, wherein the processing unit and the upstream signalbranch are configured to generate an upstream signal from a receivedupstream radio frequency signal received at the remote antenna unit,wherein the transport interface uses the upstream signal to generate theupstream transport signal. The processing unit is configured to performself-interference suppression processing on the upstream signal using,as an input thereto, a feedback signal derived from the downstream radiofrequency signal radiated from the antenna.

Another embodiment is directed a remote antenna unit for use in adistributed antenna system. The remote antenna unit comprising atransport interface to communicatively couple the remote antenna unit toa host unit included in the distributed antenna system and to receive adownstream transport signal from the host unit. The remote antenna unitfurther comprises a processing unit coupled to the transport interface,at least one downstream signal branch, and at least one upstream signalbranch. The processing unit and downstream signal branch are configuredto use the downstream transport signal to generate a downstream radiofrequency signal for radiation from an antenna associated with theremote antenna unit. The transport interface is configured tocommunicate an upstream transport signal from the remote antenna unit tothe host unit, wherein the processing unit and the upstream signalbranch are configured to generate an upstream signal from a receivedupstream radio frequency signal received at the remote antenna unit,wherein the transport interface uses the upstream signal to generate theupstream transport signal. The processing unit is configured topre-distort an input signal to the downstream signal branch fornon-linearities in the downstream signal branch using a feedback signalderived from the downstream radio frequency signal radiated from theantenna.

DRAWINGS

FIG. 1 is a block diagram of one exemplary embodiment of a distributedantenna system.

FIGS. 2-5 are block diagrams illustrating various embodiments of remoteantenna units.

FIG. 6 is a block diagram of an exemplary embodiment of a distributedantenna system that includes an expansion unit.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of one exemplary embodiment of a distributedantenna system (DAS) 100 in which the improved remote antenna unittechnology described here can be used. Although the improved remoteantenna unit technology is described here in connection with the DAS 100shown in FIG. 1, it can be used in other DAS, repeater, or distributedbase station products and systems.

The DAS 100 is used to distribute bi-directional wireless communicationsbetween one or more base stations 102 and one or more wireless devices104 (for example, mobile telephones, mobile computers, and/orcombinations thereof such as personal digital assistants (PDAs) andsmartphones). In the exemplary embodiment shown in FIG. 1, the DAS 100is used to distribute a plurality of bi-directional radio frequencybands. Also, each such radio frequency band is typically used tocommunicate multiple logical bi-directional RF channels.

The techniques described here are especially useful in connection withthe distribution of wireless communications that use licensed radiofrequency spectrum, such as cellular radio frequency communications.Examples of such cellular RF communications include cellularcommunications that support one or more of the second generation (2G),third generation (3G), and fourth generation (4G) Global System forMobile communication (GSM) family of telephony and data specificationsand standards, one or more of the second generation (2G), thirdgeneration (3G), and fourth generation (4G) Code Division MultipleAccess (CDMA) family of telephony and data specifications and standards,and/or the WIMAX family of specification and standards. In theparticular exemplary embodiment described here in connection with FIG.1, the DAS 100 is configured to handle two cellular bi-directional radiofrequency bands. In other embodiments, the DAS 100, and the improvedremote antenna unit technology described here, are used with wirelesscommunications that make use of unlicensed radio frequency spectrum suchas wireless local area networking communications that support one ormore of the IEEE 802.11 family of standards. In other embodiments,combinations of licensed and unlicensed radio frequency spectrum aredistributed.

In the exemplary embodiment described here in connection with FIG. 1,the DAS 100 is configured to distribute wireless communications that usefrequency division duplexing to implement the logical bi-directional RFbands. In other embodiments, the DAS 100 is configured to communicate atleast some wireless communications that use other duplexing techniques(such as time division duplexing, which is used, for example, in someWIMAX implementations).

Since the DAS 100 is configured to use frequency division duplexing inthis exemplary embodiment, each of the bi-directional radio frequencybands distributed by the DAS 100 includes a separate radio frequencyband for each of two directions of communications. One direction ofcommunication is from the base station 102 to a wireless device 104 andis referred to here as the “downstream” or “downlink” direction. Theother direction of communication is from the wireless device 104 to thebase station 102 and is referred to here as the “upstream” or “uplink”direction. Each of the distributed bi-directional radio frequency bandsincludes a “downstream” band in which downstream RF channels arecommunicated for that bi-directional radio frequency band and an“upstream” band in which upstream RF channels are communicated for thatbi-directional radio frequency band. The downstream and upstream bandsfor a given bi-directional radio frequency band need not be, andtypically are not, contiguous.

In the exemplary embodiment shown in FIG. 1, the DAS 100 includes a hostunit 106 and one or more remote antenna units 108. The DAS 100 shown inFIG. 1 uses one host unit 106 and three remote antenna units 108, thoughit is to be understood that other numbers of host units 106 and/orremote antenna units 108 can be used.

The host unit 106 is communicatively coupled to the one or more basestations 102 either directly (for example, via one or more coaxial cableconnections) or indirectly (for example, via one or more donor antennasand one or more bidirectional amplifiers).

In the exemplary embodiment shown in FIG. 1, the host unit 106 iscommunicatively coupled to each remote antenna units 108 over atransport communication medium or media. The transport communicationmedia can be implemented in various ways. For example, the transportcommunication media can be implemented using respective separatepoint-to-point communication links, for example, where respectiveoptical fiber or copper cabling is used to directly connect the hostunit 106 to each remote antenna unit 108. One such example is shown inFIG. 1, where the host unit 106 is directly connected to each remoteantenna unit 108 using a respective optical fiber 110. Also, in theembodiment shown in FIG. 1, a single optical fiber 110 is used toconnect the host unit 106 to each remote antenna unit 108, where wavedivision multiplexing (WDM) is used to communicate both downstream andupstream signals over the single optical fiber 110. In otherembodiments, the host unit 106 is directly connected to each remoteantenna unit 108 using more than one optical fiber (for example, usingtwo optical fibers, where one optical fiber is used for communicatingdownstream signals and the other optical fiber is used for communicatingupstream signals). Also, in other embodiments, the host unit 106 isdirectly connected to one or more of the remote antenna units 108 usingother types of communication media such a coaxial cabling (for example,RG6, RG11, or RG59 coaxial cabling), twisted-pair cabling (for example,CAT-5 or CAT-6 cabling), or wireless communications (for example,microwave or free-space optical communications).

The transport communication media can also be implemented using sharedpoint-to-multipoint communication media in addition to or instead ofusing point-to-point communication media. One example of such animplementation is where the host unit 106 is directly coupled to anintermediary unit (also sometimes referred to as an “expansion” unit),which in turn is directly coupled to multiple remote antenna units 108.One example of such a DAS 600 is shown in FIG. 6, where the host unit106 is directly connected to an expansion unit 614, which in turn isdirectly connected to the multiple remote antenna units 108. Anotherexample of a shared transport implementation is where the host unit 106is coupled to the remote antenna units using an Internet Protocol (IP)network.

Each remote antenna unit 108 includes or is coupled to at least oneantenna 112 via which the remote antenna unit 108 receives and radiatesradio frequency signals (as described in more detail below).

In general, downstream RF signals transmitted by the base station 102(also referred to here as “downstream RF signals”) are received at thehost unit 106. The downstream RF signals include both of the downstreamfrequency bands distributed by the DAS 100. In the exemplary embodimentshown in FIG. 1, the downstream RF signals for each downstream frequencyband are received on a respective downstream port of the host unit 106.The host unit 106 then generates a digital representation of thedownstream RF signals for each downstream frequency band. In oneimplementation of such an embodiment, the host unit 106 is configured todown-convert the downstream RF signals for each downstream frequencyband to a respective lower frequency band (also referred to here as an“intermediate frequency” band or “IF” band). The host unit 106 thendigitizes the resulting downstream IF signals for each downstream band,which produces digital samples of the downstream IF signals (alsoreferred to here as “downstream digital IF data”). These digital samplescan be in the form of real samples or pairs of complex samples (havingan in-phase (I) component and a quadrature (Q) component).

The host unit 106 then frames the downstream digital IF data for thedownstream frequency bands together (along with appropriate overheaddata) and communicates the frames to each of the remote antenna units108 over the respective optical fibers 110. The downstream signal thatis communicated to each remote antenna unit 108 is also referred to hereas a “downstream transport signal”. In this embodiment, the downstreamtransport signal that the host unit 106 generates for each remoteantenna unit 108 is an optical signal that is produced by opticallymodulating a downstream optical carrier with the downstream framed data(which contains the downstream digital IF data for the downstreamfrequency bands).

Each remote antenna unit 108 receives the downstream transport signalthat is communicated to that remote antenna unit 108 over a respectiveoptical fiber 110. In general, each remote antenna unit 108 demodulatesthe optical downstream transport signal (or otherwise performs anoptical-to-electrical (O/E) process) in order to recover the downstreamframed data transmitted by the host unit 106. The remote antenna unit108 then extracts the downstream digital IF data for each of thedownstream frequency bands.

In the embodiment described here in connection with FIG. 1, each remoteantenna unit 108, for each downstream frequency band, uses digitalfiltering techniques and/or digital signal processing on the downstreamdigital IF data for that downstream frequency band in order to apply oneor more of the following: pre-distortion to compensate for anynon-lineararities in the downstream signal path and phase and/oramplitude changes for beam forming or antenna steering. Then, for eachdownstream frequency band, the resulting digital IF data is applied to adigital-to-analog converter to produce a downstream analog IF signal forthat downstream frequency band. The analog IF signal for each downstreamfrequency band is then up-converted to the appropriate RF frequency bandand band-pass filtered to remove any unwanted harmonics and any otherunwanted signal components. Then, the resulting analog RF signal foreach downstream frequency band is power amplified and is ready to beradiated from at least one antenna 112 associated with the remoteantenna unit 108. Various antenna configurations can be used and aredescribed below in connection with FIGS. 2-5.

In general, in the upstream direction, upstream RF signals for eachupstream frequency band distributed by the DAS 100 are received on atleast one antenna 112 at each remote antenna unit 108. Each remoteantenna unit 108 then generates a digital representation of the upstreamRF signals for each upstream frequency band. In one implementation ofsuch an embodiment, the remote antenna unit 108 is configured todown-convert the upstream RF signals for each upstream frequency band toa respective IF band. Each remote antenna unit 108 then digitizes theresulting upstream IF signals for each downstream band, which producesdigital samples of the upstream IF signals (also referred to here as“upstream digital IF data”). These digital samples can be in the form ofreal samples or pairs of complex samples (having an in-phase (I)component and a quadrature (Q) component).

Each remote antenna unit 108, for each upstream frequency band, usesdigital filtering techniques and/or digital signal processing on theupstream digital IF data for that upstream frequency band in order toapply one or more of the following: post-distortion to compensate forany non-lineararities in the upstream signal path, phase and/oramplitude changes for beam forming or antenna steering, andself-interference and distortion suppression.

Each remote antenna unit 108 then frames the resulting processedupstream digital IF data for the upstream frequency bands together(along with appropriate overhead data) and communicates the frames tohost unit 106 over a respective optical fiber 110. The upstream signalthat is communicated to host unit 106 is also referred to here as an“upstream transport signal”. In this embodiment, the upstream transportsignal that each remote antenna unit 108 generates is an upstreamoptical signal that is produced by optically modulating an upstreamoptical carrier with the upstream framed data (which contains theupstream digital IF data for the upstream frequency bands).

The host unit 106 receives the upstream transport signals that arecommunicated from all of the remote antenna units 108 over respectiveoptical fibers 110.

The host unit 106 does the following for each of the remote antennaunits 108 from which it receives signals. The host unit 106 demodulatesthe optical upstream transport signal (or otherwise performs anoptical-to-electrical (O/E) process) in order to recover the upstreamframed data transmitted by each remote antenna unit 108. The host unit106 then extracts the upstream digital IF data for each of the upstreamfrequency bands.

For each of the upstream frequency bands, the host unit 106 digitallycombines the upstream digital IF data received from all of the remoteantenna units 108. This digital combining is performed by synchronizingthe digital samples received from all of the remote antenna units 108and then adding together (that is, digitally summing) the digitalsamples received from all of the remote antenna units 108 for eachsample period. Appropriate overflow control is used to keep theresulting sum within a desired bit resolution. The resulting combinedupstream digital IF data for each upstream frequency band is thenapplied to a respective digital-to-analog converter to produce anupstream analog IF signal for that upstream frequency band.

The resulting combined upstream analog IF signal for each upstreamfrequency band is then up-converted back to the original upstream RFfrequency and band-pass filtered to remove any unwanted harmonics andany other unwanted signal components. The resulting upstream analog RFsignal for each upstream frequency band is supplied to the base stations102 (for example, over a respective upstream port of the host unit 106).

In this way, RF signals transmitted and received by the base station 102are distributed by the DAS 100 and the resulting coverage area of thebase station 102 can be expanded.

In some embodiments of the DAS 100, a single antenna 112 is used to bothradiate (transmit) downstream RF signals and to receive upstream RFsignals. Conventionally, when a single antenna is used for bothtransmitting downstream RF signals and receiving upstream RF signals, aduplexer is used to separate and isolate the received upstream RFsignals from the transmitted downstream RF signals. When the transmitteddownstream RF signals are amplified to the relatively high output powerlevels typically used in outdoor DAS systems (for example, 10 Watts), ahigh-power duplexer (such as a relatively large and costly cavityduplexer) has historically been used in order to prevent the transmitteddownstream RF signals from inundating the components in the (receive)upstream signal paths with out-of-band power, which can cause distortionand interference in the signals produced in the upstream single paths.The use of high-power duplexers can add to the cost and size of theremote antenna unit 108. Also, the cost and size increase associatedwith conventional high-power duplexers is multiplied in applicationswhere many antennas 112 are used (for example, in MultipleInput/Multiple Output (MIMO) or antenna array applications).

FIGS. 2-5 illustrate various strategies for dealing with duplexing in aremote antenna unit 108

FIG. 2 is a block diagram of one embodiment of a remote antenna unit200. The remote antenna unit 200 is described here as being implementedfor use in the DAS 100 described above in connection with FIG. 1.

The remote antenna unit 200 includes a transport interface 202 that iscoupled to the respective optical fiber 110 that is connected to thatremote antenna unit 200. The transport interface 202 includes an opticaldemodulator that demodulates the optical downstream transport signalreceived on the optical fiber 110 from the host unit 106 in order torecover the downstream framed data transmitted by the host unit 106. Thetransport interface 202 also includes a deframer or demultiplexer toextract the downstream digital IF data for each of the downstreamfrequency bands from the downstream framed data.

The remote antenna unit 200 includes one or more downstream signalbranches 204 and one or more upstream signal branches 206. In theexemplary embodiment shown in FIG. 2, each downstream signal branch 204is used to process a respective one of the downstream frequency bandshandled by the remote antenna unit 200. Similarly, each upstream signalbranch 206 is used to process a respective one of the upstream frequencybands handled by the remote antenna unit 200.

The remote antenna unit 200 also includes a processing unit 208 that, inthe exemplary embodiment shown in FIG. 2, filters the downstream digitalIF data for each downstream frequency band. This filtering is done inorder to pre-distort the downstream digital IF data for each downstreamfrequency band in order to compensate for any non-lineararities in theassociated downstream signal branch 204. Each downstream signal branch204 includes a feedback path 210 by which a digitized version of thedownstream RF signal that is transmitted for that downstream signalbranch 204 is fed back to the processing unit 208. Each feedback path210 includes a respective RF coupler 227 to extract a portion of thedownstream RF signal transmitted for that downstream signal branch 204,a down-converter 212 to downconvert the extracted downstream RF signal,a band-pass filter 213 to remove any unwanted harmonics and any otherunwanted signal components, and an analog-to-digital converter (ADC) 214to digitize the feedback signal.

In the exemplary embodiment shown in FIG. 2, the processing unit 208uses the data provided on each feedback path 210 to adapt thepre-distortion that is applied to the downstream digital IF data foreach downstream signal branch 204 in response to changes in thedownstream signal branch 204.

Each downstream signal branch 204 includes a respectivedigital-to-analog converter (DAC) 216. The DAC 216 in each downstreamsignal branch 204 is used to convert the pre-distorted digital IF dataoutput by the processing unit 208 to a respective downstream analog IFsignal for the corresponding downstream frequency band. Each downstreamsignal branch 204 also includes an upconverter 218 that up-converts theanalog IF signal for the respective downstream frequency band to theappropriate RF frequency band. The remote antenna unit 200 includes arespective oscillator circuit 220 for each downstream signal branch 204.Each oscillator circuit 220 is configured to phase lock a local clocksignal to a reference clock and to produce one or mixing signals for useby the upconverter 218 in that downstream signal branch 204 and for thedownconverter 212 in the feedback path 210.

Each downstream signal branch 204 also includes a respective band-passfilter 224 that removes any unwanted harmonics and any other unwantedsignal components from the downstream analog RF signal output by theupconverter 218.

Each downstream signal branch 204 also includes a respective poweramplifier 226 that amplifies the downstream analog RF signal produced inthat downstream signal branch 204. In the particular embodimentdescribed here in connection with FIG. 2, the power amplifier 226 ineach downstream signal branch 204 amplifies the corresponding downstreamanalog RF signal to a power level suitable for outdoor DAS applications(for example, 10 Watts).

In the exemplary embodiment shown in FIG. 2, the remote antenna unit 200includes a single antenna 112 for each bi-directional RF band handled bythe remote antenna unit 200. That is, both the downstream analog RFsignals and the associated upstream analog RF signals for a givenbi-directional RF band are transmitted and received, respectively, usingthe same antenna 112. Also, in the exemplary embodiment shown in FIG. 2,a respective duplexer 230 is used to couple a respective downstreamsignal branch 204 and a respective upstream signal branch 206 to thecorresponding antenna 112. That is, the amplified downstream analog RFsignals output by each downstream signal branch 204 are coupled to therespective antenna 112 via a respective duplexer 230.

As noted above, each downstream signal branch 204 includes a respectivefeedback path 210 by which a digitized version of the downstream analogRF signals that are output for that downstream signal branch 204 are fedback to the processing unit 208.

In the exemplary embodiment shown in FIG. 2, RF signals received on eachantenna 112 are input to a respective upstream signal branch 206 via arespective duplexer 230. The duplexer 230 passes only the RF signals forthe upstream frequency band associated with that upstream signal branch206. Each upstream signal branch 206 includes a respective low noiseamplifier (LNA) 234 that amplifies the received upstream analog RFsignals for the associated upstream frequency band. Each upstream signalbranch 206 also includes a respective downconverter 236 thatdown-converts the amplified analog upstream RF signals output by the LNA234 in that upstream signal branch 206 to the appropriate upstream IFband. The oscillator circuit 220 associated with each upstream signalbranch 206 outputs the mixing signal used by the downconverter 236 inthat upstream signal branch 206.

Each upstream signal branch 206 also includes a respective band-passfilter 238 that removes any unwanted harmonics and any other unwantedsignal components from the output of the respective downconverter 236.Each upstream signal branch 206 also includes a respectiveanalog-to-digital converter (ADC) 240 that digitizes the respectiveanalog upstream IF signals output for that upstream signal branch 206.

The output of each ADC 240 is input to the processing unit 208. In theexemplary embodiment shown in FIG. 2, the processing unit 208 filtersthe upstream digital IF data for each upstream frequency band. Thisfiltering is done in order to post-distort the upstream digital IF datafor each upstream frequency band in order to compensate for anynon-lineararities in the associated upstream signal branch 206.

The transport interface 202 also includes a frame or multiplexer tocombine the upstream digital IF data generated for each of the upstreamfrequency bands together (along with appropriate overhead data). Thetransport interface 202 also includes an optical modulator thatgenerates an upstream optical signal for transmitting to the host unit106 on the optical fiber 110. The optical modulator in theoptical-to-electrical interface 202 generates the upstream opticalsignal by optically modulating an upstream optical carrier with theupstream framed data (which contains the upstream digital IF data forthe upstream frequency bands).

The architecture of the exemplary embodiment of a remote antenna unit200 shown in FIG. 2 is conventional in nature in that it makes use of arelatively high power amplifier 226 and a high-power duplexer 230 ineach of the downstream signal branches 204. The high-power duplexer 230provides the required degree of isolation between the relativelyhigh-power downstream RF signals transmitted from the remote antennaunit 200 and the upstream RF signals received on each such antenna 112and prevents the transmitted downstream RF signals from inundating thecomponents in the (receive) upstream signal paths 206 with out-of-bandpower. As noted above, the use of a high-power duplexer (such as acavity duplexer) can add to the cost and size of the remote antenna unit200. Also, the cost and size increase associated with conventionalhigh-power duplexers is multiplied in applications where many antennas112 are used (for example, in MIMO or antenna array applications).

FIG. 3 is a block diagram another exemplary embodiment of a remoteantenna unit 300. The remote antenna unit 300 is the same as the remoteantenna unit 200 shown in FIG. 2 except as described below. For ease ofexplanation, those components of remote antenna unit 300 that havecorresponding components in the remote antenna unit 200 are referencedin FIG. 3 (and in the following description thereof) with the samereference numerals as used in FIG. 2 for those components, though thecomponents may operate in a slightly different manner.

In the embodiment shown in FIG. 3, a low-power duplexer 230 is used tocouple each downstream signal branch 204 and its associated upstreamsignal branch 206 to its associated antenna 112. However, since thedownstream RF signals output by each downstream signal branch 204 arestill transmitted at a relatively high power, the low-power duplexer 230may not by itself provide sufficient isolation between the downstream RFsignals transmitted from the remote antenna unit 300 and the receivedupstream RF signals. To address this issue, the digitized versions ofthe downstream RF signals that are fed back to the processing unit 208(for the pre-distortion processing) are also used to suppress anyself-interference caused by the transmitted downstream RF signals. Thisis done by digitally “subtracting” or “cancelling” the transmitteddownstream RF signals from the upstream IF data that is otherwiseproduced in that upstream signal branch 206. Typically, this is doneafter the post-distortion filtering has been performed. Moreover, thedistortion caused by the components in the upstream signal branch 206being inundated with out-of-band power due to the transmitted downstreamRF signals can also be modeled and cancelled in the processing unit 208using digital signal processing techniques. The signal processing (forexample, the self-interference and distortion suppression processing)that is performed for each upstream signal branch 206 can be performedusing the digitized version of the downstream analog RF signals outputby one or more of the downstream signal branches 204. Theself-interference and distortion suppression processing that isperformed for each upstream signal branch 206 can be performed using thedigitized version of the downstream RF signal produced by only thecorresponding downstream signal branch 204 (for example, to reduce theprocessing complexity) or using the digitized version of the downstreamRF signal produced by the corresponding downstream signal branch 204 aswell those produced by one or more of the other downstream signalbranches 204 (for example, where the downstream RF signals produced bythe one or more other downstream signal branches 204 also interfere withor distort the upstream RF signal produced by that upstream signalbranch 206).

The self-interference and distortion suppression performed by theprocessing unit 208, in combination with the low-power duplexer 230, isable, in some implementations, to provide sufficient isolation betweenthe downstream RF signals and the received upstream RF signals in a morecompact and cost-effective manner.

FIG. 4 is block diagram of another exemplary embodiment of a remoteantenna unit 400. The remote antenna unit 400 is the same as the remoteantenna unit 200 shown in FIG. 2 except as described below. For ease ofexplanation, those components of remote antenna unit 400 that havecorresponding components in the remote antenna unit 200 are referencedin FIG. 4 (and in the following description thereof) with the samereference numerals as used in FIG. 2 for those components though thecomponents may operate in a slightly different manner.

In the embodiment shown in FIG. 4, instead of using a duplexer 230 tocouple each downstream signal branch 204 and its corresponding upstreamsignal branch 206 to a single, shared antenna 112, each downstreamsignal branch 204 has its own respective antenna 112-TX, and eachupstream signal branch 206 has its own respective antenna 112-RX. Noduplexers 230 are used. By using separate transmit and receive antennas112-TX and 112-RX that are spatially isolated from one another,isolation can be provided between the downstream RF signals transmittedfrom each downstream signal branch 204 and the received upstream RFsignals. However, in some applications, it may not possible to arrangethe transmit and receive antennas 112-TX and 112-RX so as to providesufficient isolation between the downstream RF signals transmitted fromeach downstream signal branch 204 and the received upstream RF signalsbased solely on spatial isolation of the antennas 112-TX and 112-RX. Theexemplary embodiment shown in FIG. 4 is directed to such a situation.

In the exemplary embodiment shown in FIG. 4, as with the exemplaryembodiment shown in FIG. 3, the digitized versions of the downstream RFsignals that are fed back to the processing unit 208 and used for insuppressing any self-interference caused by the transmitted downstreamRF signals. Moreover, as with the exemplary embodiment shown in FIG. 3,the distortion caused by the components in the upstream signal branch206 being inundated with out-of-band power due to the transmitteddownstream RF signals can also be modeled and cancelled in theprocessing unit 208 using digital signal processing techniques.

In this way, the self-interference and distortion suppression performedby the processing unit 208, in combination with the isolation providedby the arrangement of the transmit and receive antennas 112-TX and112-RX, may be able to provide sufficient isolation between thedownstream RF signals and the upstream RF signals in some situationswhere the isolation provided by the spatial arrangement of the separatetransmit and receive antennas 112-TX and 112-RX is unable to do so byitself.

Also, in the exemplary embodiment shown in FIG. 4, to reduce thelikelihood that out-of-band power from the transmitted downstream RFsignals inundate the components in the upstream signal branches 206,each upstream signal branch 206 includes a band-rejection filter (BRF)402 that rejects the frequency bands associated with the downstream RFsignals transmitted by the remote antenna unit 400. The use ofband-reject filters 402 may not be necessary in all situations. In someembodiments, a transmit band pass filter is applied after the coupler227 and before the antenna 112 in each of the downstream signal branches204.

The self-interference and distortion suppression described above canalso be used in MIMO or antenna array applications. One such example isillustrated in FIG. 5. FIG. 5 is a block diagram of another exemplaryembodiment of a remote antenna unit 500. The remote antenna unit 500 isthe same as the remote antenna unit 200 shown in FIG. 2 except asdescribed below. For ease of explanation, those components of remoteantenna unit 500 that have corresponding components in the remoteantenna unit 200 are referenced in FIG. 5 (and in the followingdescription thereof) with the same reference numerals as used in FIG. 2for those components though the components may operate in a slightlydifferent manner. Moreover, FIG. 5 has been simplified for ease ofexplanation.

The remote antenna unit 500 is similar to the one shown in FIG. 4 exceptthat the remote antenna unit 400 has been modified for a MIMO or antennaarray application where there is greater number of transmit and receiveantennas 112-TX and 112-RX used. In the exemplary embodiment shown inFIG. 5, as with the exemplary embodiment shown in FIG. 4, the digitizedversions of the downstream RF signals that are fed back to theprocessing unit 208 (for the pre-distortion processing) are also fedback to the processing unit 208 for use in providing self-interferenceand distortion suppression. The self-interference and distortionsuppression processing that is performed for each upstream signal branch206 can be performed using the digitized version of the downstream RFsignal produced by only the corresponding downstream signal branch 204(for example, to reduce the processing complexity) or using thedigitized version of the downstream RF signal produced by thecorresponding downstream signal branch 204 as well those produced by oneor more of the other downstream signal branches 204 (for example, wherethe downstream RF signals produced by the one or more other downstreamsignal branches 204 also interfere with or distort the upstream RFsignal produced by that upstream signal branch 206). In the embodimentshown in FIG. 5, the output of each downstream signal branch 204 iscoupled to a respective transmit antenna 112-TX via a respectiveisolator 510, reduces so-called “reverse intermodulaton” where thetransmitted signal from a first transmit antenna 112-TX mixes with thesignals transmitted by a second transmit antenna 112-TX to result inundesirable interference components. The isolator 510 may not benecessary in all cases, depending on, for example, the linearity of thefinal stages of the downstream signal branch 206.

Also, by using numerous transmit and receive antennas, the output powerlevels of the downstream RF signals transmitted from each remote antennaunit 108 can be reduced. This should result in a reduction in the amountof self-interference or distortion caused by the transmitted downstreamRF signals leaking into to the (receive) upstream signal branches 206and/or the components in the (receive) upstream signal branches 206being inundated with out-of-band power. As a result, in someapplications, the self-interference and distortion suppressiontechniques described above and the use of spatially isolated transmitand receive antennas 112-TX and 112-RX, may be sufficient to obviate theneed for duplexers.

More generally, the self-interference and distortion suppressiontechniques described above can be used to provide an additional amountof separation and isolation between the received upstream RF signals andthe transmitted downstream RF signals. This additional amount ofseparation and isolation may be usefully applied in applications wherethe spatial isolation of the separate transmit and receive antennas isless than optimal (for example, due to the need to achieve anomni-directional antenna structure or due to packaging concerns). Oneexample of where this may be the case is in an omni-directional antennaarray having multiple transmit and receive antennas formed on multiplesurfaces of a cube structure. Other examples of antenna modules havingpossibly less than optimal arrangements of transmit and receive antennaswhere the self-interference and distortion suppression techniquesdescribed here may be used are described in U.S. Provisional PatentApplication Ser. No. 61/495,235, filed on Jun. 9, 2011, and titled“ANTENNA MODULE HAVING INTEGRATED RADIO FREQUENCY CIRCUITRY”, which ishereby incorporated herein by reference.

In addition to the digital self-interference and distortion suppressiontechniques described above, analog self-interference suppressiontechniques can be used in which an analog version of each transmitteddownstream RF signal is delayed by 180 degrees and subtracted from thereceived upstream RF signals. One example of how such analogself-interference suppression can be performed is described in U.S.patent application Ser. No. 13/073,111, filed on Mar. 28, 2011, andtitled “EXTERNAL MOUNTED AMPLIFIERS WITH ACTIVE INTERFERENCE CANCELATIONUSING DIVERSITY ANTENNAS”, which is hereby incorporated herein byreference.

Although the embodiments shown in FIGS. 1-5 were described as beingimplemented in a particular type of digital DAS, it is to be understoodthat the self-interference and distortion suppression techniquesdescribed here can be used in other types of DAS, repeater, anddistributed base station systems and products. For example, theself-interference and distortion suppression techniques described herecan be used in a digital DAS where the signals distributed between thehost unit and the remote antenna units are digital baseband data.Examples of digital baseband formats are the formats described in theOpen Base Station Architecture Initiative (OBSAI) and Common PublicRadio Interface (CPRI) family of standards and specifications. Also, theself-interference and distortion suppression techniques described herecan be used in analog DAS and repeater products, in which case analogversions of the transmitted downstream RF signals would be fed back andalso used in each of the upstream signal branches (in a manner similarto what is described in the previous paragraph).

The components of the feedback path 210 can be used to provide digitizedversions of signals external to the remote antenna unit 108 to theprocessing unit 208. For example, one or more of the feedback paths 210includes a switch to selectively couple the input of that feedback path210 to either the coupler 227 or an antenna 112 (either directly orthrough a duplexer). In the former case (that is, when the switchcouples the input of that feedback path 210 to the coupler 227), adigitized version of the downstream RF signals for that downstreamsignal branch 204 are fed back to the processing unit 208 for thepre-distortion and self-interference and distortion suppressionprocessing described above.

In the latter case (that is, when the switch couples the input of thatfeedback path 210 to the antenna 112), signals received via the antenna112 can be fed back to the signal processing unit 208 instead of adigitized version of the downstream RF signals. This can be done, forexample, if a particular feedback path 210 is not needed for thepre-distortion and self-interference and distortion suppressionprocessing described above (for example, because the particularalgorithms used for such processing have converged to a stable state orbecause that particular downstream signal branch 204 is not being usedat that time). These fed back signals can used to determine the identityand level of co-channel cells or adjacent-channel cells.

The configuration provided in this latter case can be used for otherpurposes. For example, a specific sequence or pattern can be radiatedfrom each remote antenna unit in a DAS or from each downstream signalbranch 204 (for example, in the LTE Physical Downlink Shared Channel(PDSCH) or the HSPA PDSCH). The path-loss between the different remoteantenna units or signal branches 204 can be measured and used to controlthe base station, remote antenna unit, or downstream signal path 204,for example, for deployment or other purposes or when choosing whichunit or path to incorporate in a joint scheduling, joint beamforming orjoint MIMO transmission.

EXAMPLE EMBODIMENTS

Example 1 includes a distributed antenna system comprising: a host unit;and at least one remote antenna unit that is communicatively coupled tothe host unit; wherein the host unit is configured to communicate adownstream transport signal from the host unit to the remote antennaunit; wherein the remote antenna unit to which the downstream transportsignal is communicated uses the downstream transport signal to generatea downstream radio frequency signal for radiation from an antennaassociated with the remote antenna unit; wherein the remote antenna unitis configured to communicate an upstream transport signal from theremote antenna unit to the host unit, wherein the upstream transportsignal is generated from a received upstream radio frequency signalreceived at the remote antenna unit; and wherein the remote antenna unitis configured to perform self-interference suppression processing in anupstream signal path using, as an input thereto, a feedback signalderived from the downstream radio frequency signal radiated from theantenna.

Example 2 includes the distributed antenna system of Example 1, whereinthe remote antenna system is configured to receive the received upstreamradio frequency signal using the same antenna used to radiate thedownstream radio frequency signal.

Example 3 includes the distributed antenna system of Example 2, whereinthe remote antenna system further comprises a duplexer coupled to theantenna.

Example 4 includes the distributed antenna system of Example 3, whereinthe duplexer comprises a low-power duplexer.

Example 5 includes the distributed antenna system of Example 4, whereinthe low-power duplexer comprises a mobile handset duplexer.

Example 6 includes any of the distributed antenna systems of Examples1-5, wherein the remote antenna system is configured to radiate thedownstream radio frequency signal from a first antenna and wherein theremote antenna system is configured to receive the received upstreamradio frequency signal using a second antenna.

Example 7 includes the distributed antenna system of Example 6, whereinthe remote antenna system does not use a duplexer.

Example 8 includes any of the distributed antenna systems of Examples1-7, wherein the downstream transport signal comprises a digitizedversion of an original downstream radio frequency signal received at thehost unit and wherein the upstream transport signal comprises adigitized version of the received upstream radio frequency signalreceived at the remote antenna unit.

Example 9 includes any of the distributed antenna systems of Examples1-8, wherein at least one of the downstream transport signal and theupstream transport signal comprises digital baseband data.

Example 10 includes the distributed antenna system of Example 9, whereinthe digital baseband data comprises at least of one OBSAI digitalbaseband data or CPRI digital baseband data.

Example 11 includes any of the distributed antenna systems of Examples1-10, wherein the downstream transport signal comprises an analogversion of an original downstream radio frequency signal received at thehost unit and wherein the upstream transport signal comprises an analogversion of the received upstream radio frequency signal received at theremote antenna unit.

Example 12 includes any of the distributed antenna systems of Examples1-11, wherein a plurality of antennas is coupled to the remote antennaunit.

Example 13 includes any of the distributed antenna systems of Examples1-12, wherein the distributed antenna system is configured to distributeMIMO signals. Example 14 includes any of the distributed antenna systemsof Examples 1-13, wherein the remote antenna unit comprises a feedbackpath and a switch to selectively couple either the downstream radiofrequency signal or an external radio frequency signal to an input ofthe feedback path.

Example 15 includes a remote antenna unit for use in a distributedantenna system, the remote antenna unit comprising: a transportinterface to communicatively couple the remote antenna unit to a hostunit included in the distributed antenna system and to receive adownstream transport signal from the host unit; a processing unitcoupled to the transport interface; at least one downstream signalbranch; and at least one upstream signal branch; wherein the processingunit and downstream signal branch are configured to use the downstreamtransport signal to generate a downstream radio frequency signal forradiation from an antenna associated with the remote antenna unit;wherein the transport interface is configured to communicate an upstreamtransport signal from the remote antenna unit to the host unit, whereinthe processing unit and the upstream signal branch are configured togenerate an upstream signal from a received upstream radio frequencysignal received at the remote antenna unit, wherein the transportinterface uses the upstream signal to generate the upstream transportsignal; and wherein the processing unit is configured to performself-interference suppression processing on the upstream signal using,as an input thereto, a feedback signal derived from the downstream radiofrequency signal radiated from the antenna.

Example 16 includes the remote antenna unit of Example 15, wherein theremote antenna system is configured to receive the received upstreamradio frequency signal using the same antenna used to radiate thedownstream radio frequency signal.

Example 17 includes the remote antenna unit of Example 16, wherein theremote antenna system further comprises a duplexer coupled to theantenna.

Example 18 includes the remote antenna unit of Example 17, wherein theduplexer comprises a low-power duplexer.

Example 19 includes the remote antenna unit of Example 18, wherein thelow-power duplexer comprises a mobile handset duplexer.

Example 20 includes any of the remote antenna units of Examples 15-19,wherein the remote antenna system is configured to radiate thedownstream radio frequency signal from a first antenna and wherein theremote antenna system is configured to receive the received upstreamradio frequency signal using a second antenna.

Example 21 includes the remote antenna unit of Example 20, wherein theremote antenna system does not use a duplexer.

Example 22 includes any of the remote antenna units of Examples 15-21,wherein the downstream transport signal comprises a digitized version ofan original downstream radio frequency signal received at the host unitand wherein the upstream transport signal comprises a digitized versionof the received upstream radio frequency signal received at the remoteantenna unit.

Example 23 includes any of the remote antenna units of Examples 15-22,wherein at least one of the downstream transport signal and the upstreamtransport signal comprises digital baseband data.

Example 24 includes the remote antenna unit of Example 23, wherein thedigital baseband data comprises at least of one OBSAI digital basebanddata or CPRI digital baseband data.

Example 25 includes any of the remote antenna units of Examples 15-24,wherein the downstream transport signal comprises an analog version ofan original downstream radio frequency signal received at the host unitand wherein the upstream transport signal comprises an analog version ofthe received upstream radio frequency signal received at the remoteantenna unit.

Example 26 includes any of the remote antenna units of Examples 15-25,wherein a plurality of antennas is coupled to the remote antenna unit.

Example 27 includes any of the remote antenna units of Examples 15-26,wherein the remote antenna unit is configured to distribute MIMOsignals. Example 28 includes any of the remote antenna units of Examples15-27, wherein the remote antenna unit comprises a feedback path and aswitch to selectively couple either the downstream radio frequencysignal or an external radio frequency signal to an input of the feedbackpath.

Example 29 includes a remote antenna unit for use in a distributedantenna system, the remote antenna unit comprising: a transportinterface to communicatively couple the remote antenna unit to a hostunit included in the distributed antenna system and to receive adownstream transport signal from the host unit; a processing unitcoupled to the transport interface; at least one downstream signalbranch; and at least one upstream signal branch; wherein the processingunit and downstream signal branch are configured to use the downstreamtransport signal to generate a downstream radio frequency signal forradiation from an antenna associated with the remote antenna unit;wherein the transport interface is configured to communicate an upstreamtransport signal from the remote antenna unit to the host unit, whereinthe processing unit and the upstream signal branch are configured togenerate an upstream signal from a received upstream radio frequencysignal received at the remote antenna unit, wherein the transportinterface uses the upstream signal to generate the upstream transportsignal; and wherein the processing unit is configured to pre-distort aninput signal to the downstream signal branch for non-linearities in thedownstream signal branch using a feedback signal derived from thedownstream radio frequency signal radiated from the antenna.

Example 30 includes the remote antenna unit of Example 29, wherein theremote antenna system further comprises a duplexer coupled to theantenna.

Example 31 includes the remote antenna unit of Example 30, wherein theduplexer comprises a high-power duplexer. Example 32 includes any of theremote antenna units of Examples 29-31, wherein the remote antenna unitcomprises a feedback path and a switch to selectively couple either thedownstream radio frequency signal or an external radio frequency signalto an input of the feedback path.

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications to the described embodiments maybe made without departing from the spirit and scope of the claimedinvention.

What is claimed is:
 1. A communication system comprising: a first unit;and at least one second unit that is communicatively coupled to thefirst unit, the at least one second unit including at least oneprocessing unit, at least one downstream signal path, and at least oneupstream signal path; wherein the first unit is configured tocommunicate a downstream digital transport signal from the first unit tothe second unit, wherein the downstream digital transport signalincludes a digital representation of an original downstream radiofrequency signal received at the first unit; wherein the second unit towhich the downstream digital transport signal is communicated uses theprocessing unit and the downstream signal path to generate a downstreamradio frequency signal for radiation from an antenna associated with thesecond unit from the downstream digital transport signal; wherein thesecond unit is configured to communicate an upstream digital transportsignal from the second unit to the first unit; wherein the upstreamdigital transport signal is generated from a received upstream radiofrequency signal received at the second unit using the at least oneprocessing unit and the at least one upstream signal path, wherein theupstream digital transport signal includes a digital representation ofthe received upstream radio frequency signal received at the secondunit; and a feedback path configured to digitize the downstream radiofrequency signal to provide a digital representation of the downstreamradio frequency signal radiated from the antenna to the at least oneprocessing unit; and wherein the second unit is configured topre-distort an input signal to the downstream signal path fornon-linearities in the downstream signal path using the digitalrepresentation of the downstream radio frequency signal radiated fromthe antenna as received from the feedback path.
 2. The communicationsystem of claim 1, wherein at least one of the downstream digitaltransport signal or the upstream digital transport signal includesdigital baseband data.
 3. The communication system of claim 1, whereinat least one of the downstream digital transport signal or the upstreamdigital transport signal includes at least of one OBSAI digital basebanddata or CPRI digital baseband data.
 4. The communication system of claim1, wherein the second unit is configured to receive the receivedupstream radio frequency signal using the same antenna used to radiatethe downstream radio frequency signal.
 5. The communication system ofclaim 4, wherein the second unit further comprises at least one duplexercoupled to the antenna, wherein the at least one duplexer includes atleast one of: a low-power duplexer; a mobile handset duplexer; or ahigh-power duplexer.
 6. The communication system of claim 1, wherein:the second unit is configured to radiate the downstream radio frequencysignal from a first antenna; and the second unit is configured toreceive the received upstream radio frequency signal using a secondantenna.
 7. The communication system of claim 1, wherein: the secondunit is configured to perform self-interference suppression processingin an upstream signal path by digitally subtracting the digitalrepresentation of the downstream radio frequency signal radiated fromthe antenna from the digital representation of the received upstreamradio frequency signal as received from the feedback path.
 8. An antennaunit for use in a communication system, the antenna unit comprising: atransport interface to communicatively couple the antenna unit to aremotely located communication device included in the communicationsystem and to receive a downstream digital transport signal from theremotely located communication device, wherein the downstream digitaltransport signal includes a digital representation of an originaldownstream radio frequency signal received at the first remotely locatedcommunication device; a processing unit coupled to the transportinterface; at least one downstream signal path; and at least oneupstream signal path; wherein the processing unit and downstream signalpath are configured to use the downstream digital transport signal togenerate a downstream radio frequency signal for radiation from anantenna associated with the antenna unit; wherein the transportinterface is configured to communicate an upstream digital transportsignal from the antenna unit to the remotely located communicationdevice, wherein the processing unit and the upstream signal path areconfigured to generate an upstream signal from a received upstream radiofrequency signal received at the antenna unit, wherein the upstreamdigital transport signal includes a digital representation of thereceived upstream radio frequency signal, wherein the transportinterface uses the upstream signal to generate the upstream digitaltransport signal; and a feedback path configured to digitize thedownstream radio frequency signal to provide a digital representation ofthe downstream radio frequency signal radiated from the antenna to theprocessing unit; and wherein the processing unit is configured topre-distort an input signal to the downstream signal path fornon-linearities in the downstream signal path using the digitalrepresentation of the downstream radio frequency signal radiated fromthe antenna as received from the feedback path.
 9. The antenna unit ofclaim 8, wherein at least one of the downstream digital transport signalor the upstream digital transport signal includes digital baseband data.10. The antenna unit of claim 8, wherein at least one of the downstreamdigital transport signal or the upstream digital transport signalincludes at least of one OBSAI digital baseband data or CPRI digitalbaseband data.
 11. The antenna unit of claim 8, wherein the antenna unitis configured to receive the received upstream radio frequency signalusing the same antenna used to radiate the downstream radio frequencysignal.
 12. The antenna unit of claim 11, wherein the antenna unitfurther comprises at least one of: a low-power duplexer; and ahigh-power duplexer.
 13. The antenna unit of claim 8, wherein theantenna unit is configured to radiate the downstream radio frequencysignal from a first antenna and wherein the antenna unit is configuredto receive the received upstream radio frequency signal using a secondantenna.
 14. The antenna unit of claim 8, wherein the downstream digitaltransport signal comprises a digitized version of an original downstreamradio frequency signal received at the remotely located communicationdevice and wherein the upstream digital transport signal comprises adigitized version of the received upstream radio frequency signalreceived at the antenna unit.
 15. The antenna unit of claim 8, whereinthe downstream digital transport signal comprises an analog version ofan original downstream radio frequency signal received at the remotelylocated communication device and wherein the upstream digital transportsignal comprises an analog version of the received upstream radiofrequency signal received at the antenna unit.
 16. The antenna unit ofclaim 8, wherein a plurality of antennas is coupled to the antenna unit.17. The antenna unit of claim 8, wherein the antenna unit is configuredto distribute MIMO signals.
 18. The antenna unit of claim 8, wherein theantenna unit comprises a feedback path and a switch to selectivelycouple either the downstream radio frequency signal or an external radiofrequency signal to an input of the feedback path.
 18. The antenna unitof claim 8, wherein: the processing unit is configured to performself-interference suppression processing on the upstream signal bydigitally subtracting the digital representation of the downstream radiofrequency signal radiated from the antenna from the digitalrepresentation of the received upstream radio frequency signal asreceived from the feedback path.
 19. An antenna unit for use in acommunication system, the antenna unit comprising: a transport interfaceto communicatively couple the antenna unit to a remotely locatedcommunication device included in the communication system and to receivea downstream digital transport signal from the remotely locatedcommunication device, wherein the downstream digital transport signalincludes a digital representation of an original downstream radiofrequency signal received at the remotely located communication device;a processing unit coupled to the transport interface; at least onedownstream signal path; at least one upstream signal path; at least oneduplexer between an antenna associated with the antenna unit and both ofthe at least one downstream signal path and the at least one upstreamsignal path; wherein the processing unit and downstream signal path areconfigured to use the downstream digital transport signal to generate adownstream radio frequency signal for radiation from the antennaassociated with the antenna unit; wherein the transport interface isconfigured to communicate an upstream digital transport signal from theantenna unit to the remotely located communication device, wherein theprocessing unit and the upstream signal path are configured to generatean upstream signal from a received upstream radio frequency signalreceived at the antenna unit, wherein the upstream digital transportsignal includes a digital representation of the received upstream radiofrequency signal received at the antenna unit, wherein the transportinterface uses the upstream signal to generate the upstream digitaltransport signal; and a feedback path configured to digitize thedownstream radio frequency signal to provide a digital representation ofthe downstream radio frequency signal radiated from the antenna to theprocessing unit; a switch to selectively couple either the downstreamradio frequency signal or an external radio frequency signal to an inputof the feedback path; and wherein the processing unit is configured topre-distort an input signal to the downstream signal path fornon-linearities in the downstream signal path using the digitalrepresentation of the downstream radio frequency signal radiated fromthe antenna as received from the feedback path.
 20. The antenna unit ofclaim 19, wherein: the processing unit is configured to performself-interference suppression processing on the upstream signal bydigitally subtracting the digital representation of the downstream radiofrequency signal radiated from the antenna from the digitalrepresentation of the received upstream radio frequency signal asreceived from the feedback path.